The present invention generally relates to a spin-coater and a method of using and more particularly, relates to a spin-coater that is equipped with a self-cleaning cup for preventing the deposition and accumulation of solidified coating material on an interior surface of the coating cup and a method of using.
In the manufacturing processes for integrated circuits, a lithography process is frequently used for reproducing circuits and structures on a semiconductor substrate. As a first step in a lithography process, a photoresist layer is first coated onto a semiconductor substrate such that an image can be projected and developed on the substrate. The photoresist material is a liquid that is coated in a very thin layer on top of the semiconductor substrate. In a conventional process for applying a photoresist coating material to a semiconductor substrate, a spin coating apparatus is normally used. The spin coating apparatus is a sealed chamber constructed by an upper compartment, a lower compartment and a circular-shaped, rotating platform that has a diameter slightly smaller than the diameter of a semiconductor substrate. The rotating platform is a vacuum chuck since vacuum is applied to the platform for holding the semiconductor substrate securely during a spin coating process. The rotating platform is positioned in the coating machine such that a semiconductor substrate may be placed on top horizontally. During the coating process, the bottom or the uncoated surface of a semiconductor substrate contacts the rotating platform. A suitable vacuum is then applied to the bottom surface of the substrate such that it stays securely on the vacuum chuck even at high rotational speed. The rotating motion of the vacuum chuck is achieved by a shaft which is connected to the vacuum chuck and powered by a motor.
In a typical photoresist coating process, a desirable amount of a liquid photoresist material is first applied to a top surface of the semiconductor substrate from a liquid dispenser that is mounted on a track while the substrate is rotated at a low speed on the vacuum chuck. The photoresist liquid spread radially outward from the center of the semiconductor substrate where it is applied towards the edge of the semiconductor substrate until the entire top surface of the substrate is covered with a thin layer. Excess photoresist liquid spun off the rotating wafer during the photoresist coating process. The rotational speed of the vacuum chuck and the amount of the photoresist liquid applied at the center of the semiconductor substrate can be determined and adjusted prior to and during an application process such that a predetermined, desirable thickness of the photoresist is obtained. The rotational speed of the vacuum chuck is normally increased at the end of the application process to ensure that the entire surface of the substrate is evenly coated with the photoresist material.
A typical process flow chart illustrating a spin coating process 10 is shown in FIG. 1. In a conventional deposition process 10, a liquid material is first dispensed in step 12 by depositing a predetermined amount of liquid at or near the center of the wafer. The amount of the liquid can be suitably controlled by adjusting the flow rate through a dispensing nozzle from which the liquid is dispensed. The flow rate can, in turn, be controlled by a pressure existing in a liquid reservoir tank.
The wafer turns on a wafer pedestal at a rotational speed between 2000 and 3000 rpm when the liquid material is dispensed at the center of the wafer. The liquid material is then spun-out in step 14 by centrifugal forces from the center toward the edge of the wafer uniformly over the entire wafer surface. After all the liquid material is spun-out and the edge of the wafer is fully covered, the solvent contained in liquid has at least partially vaporized and form a solid coating on the wafer surface. After the spin-out step 14 is completed, an edge bead rinse process of step 16 is carried out at the edge of the wafer surface, i.e. an area of approximately 2xe2x80x943 mm from the edge of the wafer, to wash away material deposited at such area. At this stage of the process, the material has mostly solidified and thus the edge bead rinse process is not always effective. After the edge bead rinse step 16, the backside of the wafer is rinsed by a different jet of cleaning solvent to wash away any material deposited at undesirable locations. This is shown as step 18 in FIG. 1. The wafer is then spun-dry in step 20 to complete the coating process.
A typical apparatus 22 for coating photoresist on a semiconductor substrate is shown in FIG. 2. The apparatus 22 consists of a drain cup 28 and a rotating platform 30, i.e. a vacuum chuck, positioned at the center of the drain cup for supporting a semiconductor wafer 26 on a top surface 24 of the vacuum chuck 20. The vacuum chuck can be rotated by a shaft 32 which is connected to an electric motor (not shown). The drain cup 28 is provided with a spent photoresist drain pipe 34. The spent photoresist drain pipe 34 is used to drain away photoresist liquid that spun off the substrate during a coating operation.
In the operation of the conventional spin coater 22 of FIG. 2, the rotating platform 30 is first loaded with a semiconductor wafer 26 on top. A liquid dispenser 18 then approaches the center of the wafer 26 and applies a predetermined amount of a liquid photoresist material to the center of the substrate. The rotating platform 30 then spins to spread out the photoresist material to evenly cover the top surface of the wafer 26. Extra photoresist material 36 is thrown off the substrate surface and drained away by the drain pipe 34.
In the conventional spin-coating process of FIG. 1 utilizing the apparatus of FIG. 2, the process results in a significant waste of the coating material since a large amount of the liquid coating material is thrown off the wafer surface during wafer spinning. The liquid coating material thrown off the wafer surface adheres to an interior surface of the cup sidewall and thus forming a donut-shaped ring of solidified photoresist material on the interior surface of the sidewall. The solidified photoresist material becomes a major source of particle contamination during subsequent coating processes for the photoresist. Moreover, the solid particles of the photoresist material may also cause a blockage of a drain pipe that is normally located at a bottom wall of the cup for draining away the liquid coating material. It is a difficult task for un-blocking or cleaning the drain pipe to ensure a free flow of the spent photoresist material.
It is therefore an object of the present invention to provide a spin-coater for coating a liquid material on a wafer that does not have the drawbacks or shortcomings of the conventional spin-coaters.
It is another object of the present invention to provide a spin-coater for coating a liquid material on a wafer that is equipped with a self-cleaning coating cup.
It is a further object of the present invention to provide a spin-coater for coating a liquid material on a wafer wherein the coating cup is equipped with a solvent dispensing means.
It is another further object of the present invention to provide a spin-coater for coating a liquid material on a wafer wherein the coating cup is equipped with a solvent dispensing tube for dispensing a cleaning solvent onto an interior surface of a sidewall of the cup.
It is still another object of the present invention to provide a spin-coater for coating a liquid material on a wafer wherein the coating cup is equipped with a plurality of spray nozzles for spraying a cleaning solvent onto an interior surface of a sidewall of the cup.
It is yet another object of the present invention to provide a method for self-cleaning a spin-coater such that any accumulation of solidified coating material on an interior surface of the cup can be avoided.
It is still another further object of the present invention to provide a method for self-cleaning a spin-coater by mounting a solvent dispensing means on the coater sidewall and spraying an interior surface of the sidewall with a clearing solvent.
In accordance with the present invention, a spin-coater for coating a liquid material on a wafer equipped with a self-cleaning cup and a method for self-cleaning a spin-coater are provided.
In a preferred embodiment, a spin-coater equipped with a self-cleaning cup can be provided which includes a cup of circular shape formed by a sidewall and a bottom wall, the cup has an open top and a drain pipe through a bottom wall of the cup; a wafer pedestal situated inside the cup adapted for holding and rotating a wafer to be coated thereon; a dispensing nozzle suspended over the wafer pedestal for dispensing a liquid coating material on top of the wafer; a motor means for rotating the wafer pedestal at a preset rotational speed; and a solvent dispensing means mounted juxtaposed to an upper rim of the sidewall for dispensing a cleaning solvent on an interior surface of the sidewall to dissolve and rinse off any formation of solid contaminating particles from the splattered liquid coating material.
In the spin-coater equipped with a self-cleaning cup, the solvent dispensing means includes a solvent dispensing tube that has a plurality of apertures for dispensing the cleaning solvent, or a plurality of spray nozzles for spraying the cleaning solvent, or a plurality of spray nozzles and a solvent supply tube for delivering the cleaning solvent to the plurality of spray nozzles. The solvent dispensing means may include a solvent dispensing tube that is formed of stainless steel, or formed of Teflon. The cup of circular shape may be formed of stainless steel. The spin-coater may further include a waste solvent collection tank for collecting spent solvent from the drain pipe.
The present invention is further directed to a method for self-cleaning a spin-coater which can be carried out by the operating steps of providing a cup of circular shaped formed by a sidewall and a bottom wall, the cup has an open top and a drain pipe through the bottom wall of the cup; providing a wafer pedestal inside the cup for holding a wafer thereon; mounting a solvent dispensing means juxtaposed to an upper rim of the cup; positioning a wafer on the wafer pedestal with an active surface to be coated exposed; conducting a coating process on the active surface of the wafer; removing the wafer with the active surface coated from the cup; and dispensing a cleaning solvent onto an interior surface of the sidewall to remove any splattered coating material through the solvent dispensing means.
The method for self-cleaning a spin-coater may further include the step of mounting a solvent dispensing tube that has a plurality of apertures therethrough juxtaposed to an upper rim of the sidewall of the cup, or the step of mounting a plurality of spray nozzles for spraying a cleaning solvent therethrough juxtaposed to an upper rim of the sidewall of the cup. The method may further include the step of flowing a cleaning solvent through a conduit to the solvent dispensing means. The method may further include the step of rinsing off residual liquid coating material from the interior surface of the sidewall, or the step of dissolving solidified coating material from the interior surface of the sidewall. The method may further include the step of collecting spent solvent into a waste solvent tank from the drain pipe positioned in the cup. The method may further include the step of loading a second wafer onto the wafer pedestal after the sidewall cleaning process. The method may further include the step of forming the solvent dispensing tube in a circular shape for fitting onto the upper rim of the cup, or the step of forming the solvent dispensing tube in stainless steel, or the step of forming the solvent dispensing tube in Teflon, or the step of forming the plurality of spray nozzles in stainless steel.